In-situ combustion process for the recovery of oil



Oct. 9, 1962 M. R. J. WYLLIE 3,057,403

IN-sITU coMusToN PRocEss RoR THE RECOVERY oF on.

Filed Oct. 1'7, 1958 '/03 46a J3 49.5 I

-INV ENTOR. Macau Je.' J. WyLL/e 4 77' ORNE V Unite This inventionrelates to the production of oil and more particularly to a secondaryrecovery process for producing oil from unconsolidated formations.

One of the secondary recovery processes used to increase the amount ofoil produced from oil-bearing formations is the in-situ combustionprocess. In the conventional in-situ combustion process, anoxygen-containing gas, usually air, is injected into the pay zone at aninjection well, and oil in the formation is ignited at that well. Acombustion front moves through the pay zone from the injection well toan adjacent production well. The heat and gases released by the burningof oil in the formation reduce the viscosity of the oil and theincreased Ypressure resulting from the injection of gas into theformation drives the oil through the formation to the production well.

The conventional forward burning in-situ combustion process suffersdisadvantages which in many instances prevent its use or the productionof oil at rates sucient to justify the continued production of oil fromthe eld. The radial flow pattern from a well makes necessary highvelocities through the formation immediately adjacent to the injectionwell if satisfactory production rates are to be obtained. At leastduring the early stages of the operation, the oil pushed ahead of thecombustion front is cold and viscous. The resistance to flow,particularly `at the high rates near the well is, consequently, veryhigh. If the permeability of the formation is low, the oxygen-containinggas sometimes cannot be injected at a rate sufficient to maintain thecombustion. Immediately ahead of the combustion front is la three-phasemixture of oil, water, and gas, which further increases resistance toflow through the formation.

It has been suggested that the formation be hydraulically fracturedbefore the in-situ combustion process is performed. In this manner thepermeability of the pay zone can be greatly increased and the resistanceto ow during the initial stages of the in-situ combustion process can begreatly reduced. However, many unconsolidated formations, particularlythose which are relatively young geologically, are extremely difficultto fracture, and are especially ditiicult to fracture iat a desireddepth and in a controlled direction. Upon release of the pressure on thefracturing fluid, the unconsolidated formations frequently embed thepropping agent and close the fracture.

This invention resides in a process for the secondary recovery of oilfrom unconsolidated oil-bearing formations in which a Zone of highpermeability communicating with a Well is formed through theunconsolidated formation by reverse combustion. Then a fluid is injectedinto the formation through the zone of high permeability to drive oilfrom the pay zone to a production well. In a preferred form of thisinvention, a second zone of high permeability communicating with aproduction well and spaced from the first zone is formed by reversecombustion to provide a path through which oil moves from the formationto the production well.

Referring to the drawings:

FIGURE 1 is a diagrammatic illustration of an injection and productionwell for forming a stratum of high permeability from one well to anadjacent well by a re- Y verse combustion procedure.

tates @atene i 3,057,433 Patented Oct. 9, 1962 wells after formation ofpermeable zones connecting adjacent wells in a row for a linear driveprocess for the secondary recovery of oil from the pay zone after thehighly permeable zones have been formed through the pay zone.

Referring to FIGURE 1 of the drawings, an injection well indicatedgenerally by reference numeral 10, extends down through a cap rock 12and an oil-bearing formation designated as a pay zone 14 to a totaldepth 16. Casing 18 is run into the well and is cemented in place by acement sheath 20 in accordance with the usual practice. ln the apparatusshown in the drawings, casing 18 extends into a bed rock formation 22underlying the pay zone 14. Casing 18 and cement sheath Ztl areperforated, as indicated by reference numeral 24, at intervals from thetop to the bottom of the pay zone 14. The well 10 1s closed at the wellhead by conventional equipment illustrated in the drawing as a cap Z6.An air supply line 27 passes through the cap and extends down into thewell for injection of air into the pay Zone 14.

Referring to FIGURE 2, a field having a number of rows of Wells isillustrated. The rows are designated by letters A, B, and C. The wellsillustrated in FIGURE l are in row A. For convenience, wells andstructures in rows B and C are identified by the reference numeralscorresponding to the reference numerals of FIGURE 1, followed by thesuiiix B and C, respectively.

A `second well, indicated generally by reference numeral 2S, adjacent towell llt) in row A extends through pay zone `14 into the bed rock 22 inthe manner described for well 10. Casing 30 in well 28 also is cementedthrough the pay zone. Perforations 32 extend through the casing and thesurrounding cement sheath through the depth of pay zone 14. Well 28 isclosed at the surface by a suitable cap 34.

For ignition o-f oil in the formation adjacent well 28, an electricheater 3.6 is suspended in the well at the level of the pay zone 14.Electric heater 36 is connected with a suitable source of currentthrough lead lines 40 and 42. Although an electric heater 36 has beenillustrated in well 28 for heating the pay zone 14 adjacent the well 28,other conventional heating means such as a burner for burning mixturesof a -fuel with air can be used,

To form the permeable zone extending through the unconsolidatedformation 14, an oxygen-containing gas, preferably air, is pumped intothe well through line 27 and injected through perforations 24 into thepay zone 14. Even though the permeability of the pay zone 14 is suchthat oil cannot be moved through the `formation at practical rates, thegreater permeability of the forniation to gas than oil allows the air tothread its way to vWell 28 and enter that well through perforations 32`heater 36 can be withdrawn from well 28.

Burning of oil in the formation 14 by reverse combustion is accomplishedby continuing injection of air into the formation 14 through well 10.The combustion front moves counter to the ow of air from the vicinity ofVwell 28 toward injection well 10. Oil driven from the pay zone by thehot combustion products travels in a dlrection opposite the combustionfront and is produced at well 28. After reverse combustion proceeds fromYthe output well 28 to the well 10, continued injection ofoxygen-containing gas into the formation 14 will cause forwardcombustion from well 10 to well 28 to burn hydrocarbons remaining in thepay zone between the two wells and further increase the permeability.

The burning7 between wells 10` and 28, regardless of Whether the burningis by reverse combustion along or by reverse combustion followed byforward combustion, forms a highly permeable zone, indicated byreference numeral 46 in FIGURE 2, extending between the wells. Theprocess described above for Wells 10 and 28 is repeated for wells in rowB to form a permeable Zone 46B between wells 10B and 28B. The procedurecan similarly be repeated for Wells in row C to `form a permeable zoneindicated by reference numeral 46C between wells 10C and 28C. Thepermeable zone extending from Wells l0 to 28 can be made to extend inboth directions from Wells 10 and 28, for example to adjacent wells 48and 49, to connect all of the wells in a single row, if desired. Afterthe formation of a permeable zone connecting adjacent Wells in a row, anoxygen-containing gas is injected into the pay Zone 14 through one ormore and preferably all of the wells in a single row in the field. Forpurposes of illustration, the wells 10, Z8, 48, and 49 in row Arand theWells 10C, 28C, 48C, and 49C in row C are injection wells. Oil in thepay Zone is then ignited and the continued injection ofoxygen-containing gas, preferably air, through wells in rows A and Cburns oil in therformation and supplies energy to move oil through thepay Zone 14 to the permeabie Zone 46B in row B. The oil then fiowsreadily through the permeable zone 46B into wells `ltBB and 23B lfromwhich it is lifted to the surface.

The combustion to move the oil from the formation 14- towards permeableZone 4B for delivery to the wells can be either forward or reversecombustion. Ordinarily because of the low permeability of the pay Zonesin which this invention is most useful, reverse combustion to producethe oil from the pay zone yor to warm it prior to the initiation of aforward combustion phase is preferred. Ignition in permeable Zone 46Bcan be accomplished by injecting a mixture of a combustible gas and airinto permeable stratum 46B through wells in row B and igniting themixture to heat the formation to a temperature at which ignition willoccur upon contact with air or other oxygen-containing gas injected intothe pay zone in row A or rows A and C. A preferred method Of ignition isto inject a mixture of a combustible gas and air through the wells inrow A and ignite that mixture as it enters the permeable zone 46B bymeans o=f an electric spark. After ignition, the injection of acombustible gas through the wells in row A is discontinued while theinjection of the oxygen-containing gas is continued. In the arrangementshown in FIGURE 2, injection of oxygen-containing gas into the pay zonethrough wells in row C is continued simultaneously with the injection ofoxygen-containing gas through the wells in row A.

The linear flow from permeable zones 46 and 46C to permeable zone 46Ballows substantially complete removal of oil from the oil-bearingformation. Although resistance to flow through the oil-bearing formationbetween -the permeable zones will interfere with the fiow f oil inforward burning or gas repressuring secondary recovery procedures, thehighly permeable zones extending to the wells greatly reduce the totalresistance to flow. Oil can flow at high rates through the highlypermeable zones directly into the Wells.

In an example of this process, in an oil field in which the Wells arearranged in a five spot pattern, three boreholes are drilled 660 feetapart in a line to a total depth of 1510, 1515, and 1522 feet through apay zone 78 feet thick. Seven inch casing is set through the pay Zoneand cemented in the conventional manner. The strings `of casing areperforated at the intervals 1445 to 1500 feet,

1450 to 1505 feet and 1455 to 1515 feet, respectively. A mixure of airand lease gas is injected into the middle well and ignited at the otherwells by means of an electric spark. After ignition, injection of thelease gas is stopped and the injection of air is continued at a rate ofone and one-half million standard cubic feet per day. Reverse combustionis continued for 300 days and then converted to forward combustion inthe vicinity of the first well by increasing the rate of air injectionto three million standard cubic feet per day, and continued for 30 days.The procedure is repeated in three directly offset wells in an adjacentline.

A mixture of lease gas and air in a ratio of 15 volumes of air pervolume of lease gas is injected into three wells in the first line at atotal rate of ten million standard cubic feet per day. When the gasmixture breaks through into adjacent line of wells, the mixture isignited. Injection of the mixture of gases is continued forten days,after which the injection of the lease gas is stopped. The injection ofair is continued at .the rate of ten million standard cubic feet per daywhile the oil is produced from the wells in the second line.

The initial reverse combustion steps are highly effective in increasingthe permeability of the unconsolidated formations and reducing theresistance to fiow of heavy oils present in the oil-bearing formation.In addition to heating oil throughout the permeable zone of theformation, any clays present in that zone tend to be irreversiblydehydrated thereby preventing their swelling upon contact with Water.The heat from the reverse combustion process raises the temperature ofthe oil in the formation and decreases its viscosity. The reversecombustion procedure is particularly effective in fields containing Veryheavy oils. It is possible in many such fields to cause flow of gas fromone well to an adjacent well without displacing oil from the formation,whereas displacement of the cold oil from the formation is not feasible.By forming substantially parallel Zones of high permeability joiningwells in adjacent lines, a second secondary recovery step using a lineariiow pattern is made possible. The linear fiow pattern and relativelyshort dista-nce between the .permeable zone allow low fluxes (vol/sq.ft./hr.) for the injected air and reduced oxygen absorption insubsequent reverse combustion steps. The process of this invention isparticularly advantageous in producing oil from unconsolidatedformations of low permeability in which the high resistance to flowmakes the usual secondary recovery processes ineffective.

I claim:

l. A process for the production of oil from a sub-surface oil-bearingformation penetrated by a plurality of wells in a series ofsubstantially parallel rows comprising injecting an oxygen-containinggas into the oil-bearing formation through a first well in a first rowand withdrawing gas from a second well in the first row, igniting oil in-the formation at said second well, continuing the injection ofoxygen-containing gas at the first well to cause reverse combustion toproceed from the second vwell to the first well to form a firstpermeable zone through a portion `of the oil-bearing formationcommunicating `with said first and second wells in the first row,thereafter injectingan oxygen-containing gas into the oil-bearingformation through a first well in a second row of wells spaced from thefirst row of wells and withdrawing gas from a second well in said secondrow of wells, igniting `oil in the formation at said second well in saidsecond Vdrawing fluids from a well penetrating the second permeable zoneto displace loil through the oil-bearing formation in a directionsubstantially perpendicular to the rows of wells toward the secondpermeable zone.

2. A process for the production of oil from a subsurface oil-bearingformation penetrated by a plurality of wells in a series ofsubstantially parallel rows comprising injecting an oxygen-containinggas into the oil-bearing formation through a first well in a first rowyand withdrawing gas from a second well in the first row, igniting oilin the formation at said second well, continuing the injection ofOxygen-containing gas at the first well to cause reverse combustion toproceed from the second well to` the first well to form a firstpermeable zone through a portion of the oil-bearing -formationcommunicating with said first and second wells in the first row,thereafter injecting an oxygen-containing gas into the oil-bearingformation through a first well in a second row of wells spaced from thefirst row of wells and withdrawing gas from a second well in said secondrow of wells, igniting oil in the forniation at said second well in saidsecond row, continuing the injection of oxygen-containing gas into thefirst well in the second row of wells to cause reverse combustion toproceed from the second well in said second row to the first well insaid second row whereby a second permeable zone is formed spaced fromand su-bstantially parallel to the first permeable zone, then injectingan oxygen-containing gas into the first permeable zone and withdrawingfluids through a well penetrating the second permeable zone to establishflow `through the oil-bearing formation between the first and ysecondpermeable zone substantially perpendicular to the rows of wells,igniting oil in the formation Iadjacent the second permeable zone,continuing the injection of the oxygen-containing gas into the firstpermeable zone to cause reverse combustion to proceed from the secondpermeable zone to the first permeable zone, and lifting fluids to thesurface through a well penetrating the second permeable zone.

3. A process for the production of oil from a sub- -surface oil-bearingformation penetrated by a plurality of wells in a series ofsubstantially parallel rows comprising injecting an oxygen-containingrgas into the oil- -bearing formation through the first well in a firstrow and withdrawing gas from a second well in the first row, ignitingoil in the formation at said second well, continuing the injection ofoxygen-containing gas at the first well to cause reverse combustion toproceed from the second well to the first well to form a first permeablezone through a portion of the oil-bearing formation communicating withsaid first and second wells in the first row, thereafter injecting anoxygen-containing gas into the oil-bearing formation through a firstwell in a second row of wells spaced from the first row of wells andwithdrawing gas from a second well in said second row of well-s,igniting oil in the formation at said second well in said second row,continuing the injection of oxygen-containing gas into the first well inthe second row of wells to cause reverse combustion Ito proceed from thesecond well in said second row to the first well in said second rowwhereby a second permeable zone is formed spaced from and substantiallyparallel to the first permeable zone, then injecting anoxygen-containing gas into the first permeable zone and withdrawingfiuids through a well penetrating the second permeable zone to establishfiow through the oil-bearing formation perpendicular to the rows ofwells, igniting oil in the formation between the first permeable zoneand the second permeable zone, continuing injection of theoxygen-containing gas into the first permeable zone to cause combustionof the oil between the two permeable zones and drive oil through theformation to -the second permeable zone and to a well penetrating thesecond permeable zone through which fiuids are withdrawn.

4. A process for the production of oil from a subsurface oil-bearingformation penetrated by a plurality of wells in a series ofsubstantially parallel rows comprising injecting an oxygen-containinggas into `the oilbearing formation through a first well in a first rowand withdrawing gas from a second well in the first row, igniting oil inthe formation at said second well, continuing Ithe injection ofoxygen-containing Agas at the first well to cause reverse combustion toproceed from the second well to the first well to form a first permeablezone through a portion of the oil-bearing formation communicating withsaid first and second wells in the first row, thereafter injecting anoxygen-containing gas into the oilbearing formation through a first wellin a second row of wells spaced from the first row of Wells andwithdrawing gas from a second well in said second row of wells, ignitingoil in the formation at said second well in said second row, continuingthe injection of oxygen-containing gas into the first well in the secondrow of wells to cause reverse combustion to proceed from the second wellin said second row to the first well in said second row where-by asecond permeable zone is formed spaced from and substantially parallelto the first permeable zone, then injecting an oxygen-containing gasinto the first permeable zone and withdrawing fluids through a wellpenetrating the second permeable zone to establish flow through theformation substantially perpendicular to the rows of wells, igniting oilin the formation adjacent the first permeable zone, and continuing theinjection of the oxygen-containing gas into the first permeable zone tocause forward burning to proceed from the first permeable zone to thesecond permeable zone.

5. A process for the production of oil from a subsurface oil-bearingformation penetrated :by -a plurality of wells in a series ofsubstantially parallel rows comprising injecting an oxygen-containinggas into the oil-bearing formation through a first well in a first rowand withdrawing gas from a second well in the first row, igniting oil inthe formation at said second well, continuing the injection ofoxygen-containing gas at the first well to cause reverse combustion toproceed from the second well -to the first well to form a firstpermeable zone through a portion of the oil-bearing formationcommunicating with said first and second wells in the first row,thereafter injecting an oxygen-containing gas into the oil-bearingformation through a first well in a second row of wells spaced from thefirst row of wells and withdrawing gas from a second well in said secondrow of wells, igniting oil in the formation at said second well in saidsecond row, continuing the injection of oxygen-containing gas into thefirst well in the second row of wells to cause reverse combustion toproceed from the second well in said second row to the first well insaid second row whereby a second permeable zone is formed spaced fromand substantially parallel to Ithe first permeable zone, then injectinga mixture of an oxygen-containing gas and a gaseous fuel into the firstpermeable zone and withdrawing fiuids through a well penetrating thesecond permeable zone to establish fiow through the formationsubstantially perpendicular to the rows of wells, igniting the mixtureof oxygen-containing gas and fuel gas in the second permeable zone toignite oil in the formation adjacent the second permeable zone,discontinuing -the injection of the fuel gas and continuing theinjection of the oxygen-containing gas to cause reverse combustion fromthe second permeable zone to the first permeable zone and lifting fluidsto the surface through a well in the second row of wells.

References Cited in the file of this patent UNITED STATES PATENTS2,793,696 Morse May 28, 1957 2,888,987 Parker June 2, 1959 2,899,186Crawford Aug. 11, 1959 2,906,340 Herzog Sept. 29, 1959

